Overexpression and characterization of recombinant hCGβ-LTB vaccine in fed-batch culture of yeast Pichia pastoris

Recombinant HCGβ-LTB expressed in the yeast, holds a significant promise as a contraceptive vaccine for women. It induces bio-effective anti-hCG antibodies, which can potentially prevent pregnancy by neutralizing the hCG hormone crucial for establishment and maintenance of pregnancy. The vaccine produced in shake-flask culture and administered along with adjuvant Mycobacterium indicus pranii (MIP) induces high anti-hCG titres in mice of different genetic strains. This study aimed to produce the vaccine in high cell density culture in a bioreactor and assess its consistency and efficacy compared to shake-flask production. A fed-batch culture increased the cell biomass nearly 6.5 folds higher than the shake-flask culture. Increase in specific-activity by a factor of 1.7 resulted in almost 11-fold higher volumetric activity. Characterization of the purified protein and immunogenicity studies conducted in mice demonstrated that it was comparable to protein made in shake-flask. This study shows that hCGβ-LTB vaccine can be produced cost-effectively with consistent characteristics in high cell density cultures of Pichia pastoris on a large-scale for eventual pre-clinical/clinical studies.